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How to Diagnose Problems with Your Car

Learn what every shake, rattle, and roll means so that a car mechanic can’t tell you that a cracked hose is a major transmission meltdown.


  • Step 1: Get an OBD If your car was made after 1995, invest in an on-board diagnostics reader, which you can find online or at an auto parts store starting at about $50. (Actron is a popular brand.) When your car begins acting up, just plug the reader into a port located under your dashboard and it will identify the problem.
  • TIP: Expensive readers will spell out what’s wrong, while cheaper models will give you a code that you’ll have to translate.
  • Step 2: Read smoke signals Learn what smoke coming from your tailpipe means. Black smoke indicates your fuel calibration is off; blue means you’re burning too much oil; white means coolant is leaking. Smoke coming from the hood is likely from a crack in one of the radiator hoses; let the car cool down before you pop the hood.
  • TIP: If smoke is coming from your hood and you’ve recently had your oil checked, see if the service station attendant forgot to put the oil cap back on.
  • Step 3: Know your signs Know which signs mean big trouble, and which mean you just need to refill one of your fluids. An engine that moans when you steer likely needs power steering fluid; a brake that sinks to the floor when you stop needs brake fluid. But a clattering engine requires immediate attention -- pull over, turn off the car, and call for roadside assistance.
  • Step 4: Know your screeches Know your screeches. A car that screeches when you accelerate may just need a new fan belt, one that screeches when you steer may simply need the power steering belt adjusted, and screeching when you slow down means it’s time for new brake pads.
  • Step 5: Name that noise Recognize the noises that indicate an easy fix. A clicking wheel may just have a loose hubcap, or a stone stuck in it; a clicking engine could mean you’ve got a bad valve; a loud, rapid rat-tat-tat sound of metal slapping metal could be a damaged or loose fan blade; a hiss usually means a leaking hose.
  • Step 6: Pinpoint that thump If you hear thumping noises coming from the back of your car, check to see if something in your trunk is rattling around before you panic. If the sound is more like a rumble, and it gets worse when you turn, your wheel bearings may be worn out.
  • Step 7: Decipher that squeal If your engine is squealing like a pig, it’s probably just a loose belt. And if you just drove through water, it could be that the belts are wet and the noise will go away as soon as they dry.
  • Step 8: Identify clear liquids If you notice that your car is dripping a clear fluid, see if it’s slippery. If it is, you might be leaking brake fluid, a situation that needs to be checked immediately. If not, it’s probably just water coming from the air conditioning unit, which is normal. Clear fluid can also be gasoline, but you’ll know that from the distinct smell.
  • TIP: Some brake fluids have a yellowish tint.
  • Step 9: Decipher colors Know the colors of your car fluids in case you ever see a puddle of them beneath your car. Coolant is usually green, but it can be red or brownish red as well, and the color is translucent. An opaque dark red color means you’re leaking either transmission or power steering fluid. Black, brown, or amber fluid is engine or gear oil.
  • Step 10: Know the serious sounds Know the sounds that mean serious business. If your engine gives off a knocking sound that gets faster as you drive, roars when you speed up, or whines in general, see a technician as soon as possible.
  • FACT: One study of auto repair shops found that 52% of repair charges represented completely unnecessary work!

You Will Need

  • An on-board diagnostics reader (OBD)
  • Some basic car knowledge

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